An optical thin film used in optical products includes a plurality of layers having different refractive indexes. Each layer is stacked onto a substrate to obtain various types of optical characteristics, such as an antireflective characteristic, a filtering characteristic, and a reflective characteristic. For example, an oxide of a metal such as tantalum, titanium, niobium, and zirconium is used as a high refractive index material. For example, a silicon oxide or magnesium fluoride is used as the low refractive index material.
The manufacturing operation for an optical thin film includes the so-called sputtering process, which uses a plurality of targets formed by dielectrics of a low refractive index material, high refractive index material, or the like and sequentially deposits sputtering grains released from the targets onto the substrate. Such type of sputtering process includes a magnetron sputtering process, which implants plasma near the surface of the target, and a high frequency sputtering process, which applies high frequency power to the targets.
When using a dielectric as the target material for the sputtering method, the charge accumulated in the dielectric has a tendency to cause abnormal discharge. Thus, the high frequency sputtering process is generally selected. However, when using the high frequency sputtering process, in comparison to the magnetron sputtering process, the plasma density has a tendency to vary more easily when the substrate undergoes transportation and the like and the film forming speed may be greatly decreased. Various proposals have been made in the prior art for the manufacturing method of the optical thin film to solve such problems.
A film formation device described in patent document 1 arranges a rotary drum inside a vacuum chamber and forms a plurality of processing regions inside the vacuum chamber in the circumferential direction of the rotary drum. For example, a processing region for forming a metal layer using the magnetron sputtering process, a processing region for forming a silicon layer using the magnetron sputtering process, and a processing region for generating oxygen plasma and performing an oxidation process are formed around the rotary drum. The film formation device described in patent document 1 rotates the rotary drum to selectively and repetitively perform the formation of a metal layer, the formation of a silicon layer, and the oxidation of each layer on the surface of a substrate mounted on the rotary drum. Patent document 1 allows for the deposition of the high refractive index material and the deposition of the low refractive index material to be accelerated under stable deposition conditions. This increases the stability and speed of the process for forming the optical thin film.
The optical characteristics of optical thin films used in optical products easily deteriorate when various types of liquids from the exterior collect on the surface of the thin film. Thus, it is desirable that a liquid repellent film having liquid repellency for repelling various types of liquids be formed on the surface of the optical thin film. In an operation for forming the liquid repellent film, a dipping process is first performed using a silane coupling agent, which contains a liquid repellent group for repelling liquid and a hydrolytic condensation group, to form a dipping layer containing the silane coupling agent on the surface of the optical thin film. Subsequently, water is supplied to the dipping layer formed on the optical thin film to polycondense the silane coupling agent and thereby form the liquid repellent film.
However, when forming the liquid repellent film in the above-described operation, water acting as a polycondensation initiator is supplied from the surface of the dipping layer. This initiates polycondensation of the surface of the dipping layer before the interior of the dipping layer and advances polymerization of the dipping layer thereby causing high polymerization of the dipping layer. As a result, it becomes difficult for the water to reach the interior of the dipping layer and the vicinity of the substrate. This lowers the polymerization rate of the silane coupling agent accordingly and slows reaction with the substrate. Thus, it becomes difficult to obtain mechanical strength of the liquid repellent film and adhesion or the like between the liquid repellent film and optical thin-film. This may result in separation of the liquid repellent film.